The following requirements describe some of the major features of a recording material used in ink jet printing:
1. Sufficient ink absorbing capacity and ink receptivity of the receiving layer to prevent the ink from streaking and from running down during printing, even under conditions where several droplets are deposited in a rapid sequence onto the same spot.
2. Fast drying of the layer surface after printing of the image leading to prints free from tackiness.
3. Excellent colour rendition, no change of the hue of the picture with time.
4. Surface with high gloss.
5. In the case of transparencies, clear, transparent, scatter free receiving layers.
6. Resistance of the image surface of the image to rubbing.
7. Excellent waterfastness of the produced images.
8. Excellent light fastness of the printed images.
9. Excellent archival stability.
10. Excellent physical and handling properties.
The particular problem of waterfastness has in the past been addressed by a wide variety of techniques. Thus solutions to the problem have been proposed for by specific formulations of the inks or alternatively in many cases by specific modifications of the receiving layers. The two approaches have in many cases been combined.
One attempt to improve waterfastness has been the use of reactive dyes. So for instance in U.S. Pat. No. 4,443,223 (Kissling et al.), U.S. Pat. No. 5,098,475 (Winnik et al.), U.S. Pat. No. 5,074,914 (Shirotz et al.), U.S. Pat. No. 5,230,733 (Pawlowski et al.), JSDC (1993) 109, 147 (S. O. Aston et al.) and references cited therein. Although some improvement has been achieved by this technique no satisfactory results can in general be obtained due to the fact that the conditions which are possible in practice in a printing environment are less than optimal and do in general not suffice to achieve reaction of these dyes with given binders. Inks based on colloidal dye dispersions and polymers in inks have been proposed so for in instance in U.S. Pat. No. 5,100,471 (Wink et al.), U.S. Pat. No. 5,017,644 (Fuller et al.), U.S. Pat. No. 4,990,186 (Jones et al.), U.S. Pat. No. 4,597,794 (Kasha et al.), U.S. Pat. No. 4,210,566 (Murrey), U.S. Pat. No. 4,136,076 (Dennison et al.), U.S. Pat. No. 5,224,987 (Matrick et al.), U.S. Pat. No. 5,180,425 (Matrick et al.) and U.S. Pat. No. 4,246,154 (Yao et al.). Inks based on colloidal dyes as well as on hot melt inks, although yielding images with good waterfastness and good light stability, do in many cases lead to images which are not transparent and therefore less suited to be used for projections.
Often involved modifications of the inks have the tendency to give inks liable to show precipitates upon prolonged storage. Such precipitates subsequently tend to clog the nozzles of ink jet printer.
The major attempt to achieve waterfastness in receiving layers has been via the use of polymers, particular cationic polymers in conjunction with inks containing acidic dyes.
U.S. Pat. No. 4,877,680 describes cationic polymers together with neutral binders. Cationically modified polyvinyl alcohol has been described in U.S. Pat. No. 4,783,376. U.S. Pat. No. 4,575,465 claims quaternised polyvinyl pyridine to achieve waterfastness. U.S. Pat. No. 4,554,181 describes the use of a combination of cationic polymers and polyvalent metal salts since only such combinations and not the single elements tend to provide the sought for properties.
Although good waterfastness can in general be obtained with a wide variety of cationic polymers they tend to show a severe drawback in that they impair the light fastness of the printed images.
The introduction of inorganic pigments, fillers, minerals, metal salts and metal oxides have been proposed. U.S. Pat. No. 4,116,910 (Rudolphy et al.) propose the use of derivatives of metals of Group II of the periodic table together with natural resin. JP 6025 7285 (Nakadsugawa et al.) claims an improvement of light stability by addition of transition metal oxides. Waterfastness can preferentially be achieved by addition of metal oxides together with cationic pigments or polymers to the receiving layers. U.S. Pat. No. 5,104,730 (Misuda et al.) and U.S. Pat. No. 4,879,166 (Misuda et al.) describe porous recording sheets where the porous layer is mainly made of pseudo boehmite, a colloidal aluminium oxide hydroxide. Although in general satisfactory waterfastness can be achieved the layers obtained by this method are slightly opaque and show severe tendency to become brittle with time and on exposure to light. All the above mentioned solutions fulfil only partly the requirements of image receiving layers for modern ink jet printing. In many cases these solutions lead moreover only to material suitable for quite restricted applications. Improvements incorporated into ink receiving layers, widely applicable to modern ink jet printing technology, are therefore the scope of this invention.